1. Field of the Invention
The present invention relates to a method for implementing a Performance Monitoring function according to data retrieved through FEC (Forward Error Correction), in a telecommunication network.
2. Description of the Prior Art
The Forward Error Correction (FEC) mechanism is known in the transmission field as a methodology for correcting transmission errors, for example in the synchronous systems, such as SDH (Synchronous Digital Hierarchy) or SONET (Synchronous Optical NETwork), or in the optical systems, such as OTN (Optical Transmission Network), which is based on the insertion of redundancy bits at transmission and on the consequent errors correction at the receiving side.
Substantially, there are two types of FEC:                in-band FEC: the redundancy bits are transported within the frame (in SDH, for instance, they are in the header SOH, Section OverHead) so that the frame bit-rate is not increased;        out-of-band FEC: the redundancy bits are transported in an auxiliary frame which is added to the frame itself, thus slightly increasing the frame bit-rate.        
The properties of the FEC system are well known to the man skilled in the art, being also subject of the Standards ITU-T G.707, G.709 and G.975.
It is also known the need of defining a procedure for determining PM (Performance Monitoring), which consists in the evaluation of the path (link) quality, based on the evaluation of the result of the FEC procedure.
The known procedures for the PM determination based on the data of FEC (see Standard ITU-T G.optperf, which is going to be defined) foresee the independent use of two uncorrelated sets of primitive counters for corrected errors in respective information blocks and uncorrected blocks, which are hereunder defined.
The arising problem is that this approach does not deliver sufficient information about the real transmission quality of the path (link). In fact, under conditions of bad transmission quality, the error counter does not provide reliable data as it refers to information blocks which can not be corrected through the FEC procedure; furthermore, also the evaluation of BER (Bit Error Rate) is not possible.